To determine whether a family history of osteoporosis identifies individuals with low bone mineral density (BMD), we studied 1477 white elderly (aged 60-89 years), noninstitutionalized ambulatory men (n = 600) and women (n = 877) from the Rancho Bernardo, California cohort. Family history data on biologic parents and full sisters were obtained by questionnaire. BMD of the lumbar spine and hip was measured using dual-energy x-ray absorptiometry. After adjustment for age, body mass index, history of cigarette smoking, thiazide use, and estrogen use, men and women with a family history of osteoporosis had lower BMD than those with a negative family history. In men, a positive family history was associated with lower BMD at the hip (p = 0.01), whereas in women a significant association was observed for the spine (p = 0.02). BMD decreased in a stepwise fashion with an increasing number of family members with a history of osteoporosis. Analysis of the effect of parental history of osteoporosis on BMD showed a significant relation between paternal (but not maternal) history and lumbar spine BMD in both sexes and a significant relation between maternal (but not paternal) history and hip BMD only in men. The relative risk of having categoric osteopenia was highest in those whose fathers had a history of osteoporosis (RR 2.16, 95% CI = 1.38-3.37). A similar association was found for subjects with fractures. These results were not explained by differential awareness of family history in individuals with known osteoporosis, because the prevalence of family history was unrelated to personal history of osteoporosis in men and only weakly related in women.(ABSTRACT TRUNCATED AT 250 WORDS)